Filtering and forwarding frames at an optical network node

ABSTRACT

An optical line terminal (OLT) monitors and controls communications with a plurality of optical nodes (ONs), such as optical network units (ONUs) and/or optical network terminators (ONTs), within a passive optical network (PON), such as, but not exclusively, an Ethernet-based passive optical node (EPON). A tagging mechanism is implemented to identify an origin ON that introduces a frame into the PON segment linking the origin ON with the OLT. The origin ON produces a PON tag to associate its identifier (ON_ID) to the frame. The PON tag facilitates filtering and forwarding operations, and enables the physical layer interface (PHY) to the PON segment to emulate a point-to-point and/or shared communications link. The PON tag allows a MAC control layer to create virtual ports to traffic incoming and outgoing optical signals, and supply the virtual ports to a forwarding entity for frame filtering and forwarding. The PON tag also allows an OLT and ON to track the origination and/or destination of a frame within the PON segment, and accept or reject the frame based on the contents of the PON tag.

This application is a continuation of U.S. patent application Ser. No.10/316,181, filed Dec. 11, 2002, by Sala et al., entitled “filtering andForwarding Frames within an Optical Network,” incorporated herein byreference. This application also claims the benefit of U.S. ProvisionalApplication No. 60/339,442, filed Dec. 14, 2001, by Sala et al.,entitled “EPON Compliance Framework and Solution,” incorporated hereinby reference; U.S. Provisional Application No. 60/367,317, filed Mar.26, 2002, by Sala et al., entitled “EPON Compliance Framework andSolution,” incorporated herein by reference; and U.S. ProvisionalApplication No. 60/393,096, filed Jul. 3, 2002, by Gummalla et al.,entitled “System and Method for Supporting Security and Other Servicesin an Ethernet Passive Optical Network,” incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to communications networking,and more specifically, to filtering and forwarding frames in an opticalnetwork.

2. Related Art

In regards to communications networks, there is a continuous challengeto achieve an optimal balance among various network characteristics.Such characteristics include bandwidth demand and quality of serviceparameters, such as latency, loss, or priority. For example,data-overcable networks presently are expanding the variety of servicestraditionally provided to subscribers. In addition to televisionbroadcasts, cable providers are offering telephony, messaging, andInternet services. As a result, additional bandwidth is needed tosupport the timely delivery of these services. Moreover, traditionalcable broadcasts primarily require one-way communication from a cableservice provider to a subscriber's home. As interactive or personaltelevision services and other nontraditional cable services continue tobe offered, communications media used to support one-way communicationsmust now contend with an increased demand for bi-directionalcommunications.

Optical networks are evolving as a solution to bandwidth limitationsprevalent on communication networks. For example, a passive opticalnetwork (PON) can be built to gain bandwidth efficiency and reduceprotocol overhead. A typical PON consists of an optical line terminal(OLT) that manages communications with a plurality of optical networkunits (ONUs). Conventional PON topology has a shared upstream and abroadcast downstream. The ONUs have the opportunity to listen to thedownstream broadcasts. However, the OLT uses time division multiplexingto enable the ONUs to send frames containing data and/or requests inassigned slots in the upstream. Frames sent in the upstream from one ONUare not seen by the other ONUs.

The communications path between an OLT and its ONUs is referred to as aPON segment. A conventional PON segment is neither a point-to-point(P2P) segment nor a shared segment. In a typical shared segment, a frameis seen by all attached devices. In a PON segment, however, frames onthe upstream are not seen by any other device. When upstream framesarrive at the OLT from a PON segment, the frames are processed, filteredand forwarded to the next destination. The OLT uses a forwarding entity(such as, a bridge or router) to execute the filtering and forwardingoperations. Conventional forwarding entities only support P2P or sharedsegments, and as discussed, conventional PON segments are neither.Therefore, conventional forwarding entities assume all devices linked toone of its ports have seen any frame delivered to that port. As aresult, the forwarding entity will not send a frame back to the portthat delivered the frame, even if a destination is an end user linked tothe incoming PON segment.

Therefore, a method and system are needed to address the above problems.

SUMMARY OF THE INVENTION

The present invention solves the above problems by providing a method,system, and computer program product for filtering and forwarding frameswithin an optical network. In the preferred embodiment, the opticalnetwork is a passive optical network (PON) such as, but not exclusively,an Ethernet-based passive optical node (EPON). A tagging mechanism isimplemented to uniquely identify an origin optical node that introducesa frame into the PON segment linking the origin optical node with anupstream optical line terminal (OLT). The origin optical node produces aPON tag comprising its optical node identifier (ON_ID). In anembodiment, the PON tag is included in the header of the frame toproduce a PON-tagged frame.

In an embodiment, the PON tag includes a PON tag type field and a PONtag control information field. The PON tag type field indicates thepresence of a PON tag. The PON tag control information field contains anON_ID, which is typically an ON_ID for the origin optical node. When aframe is first introduced into a PON segment, the origin optical nodetags the frame with a PON tag carrying its own ON_ID.

In an embodiment, the PON tag control information field also includesfields for designating a mode and filtering operation. The mode fieldspecifies whether the frame is to be, or has been, transported over apoint-to-point (P2P) communications path to a single destination, or ashared communications path to multiple destinations. The filteringoperation field specifies whether the frame is to be filtered by asource identifier or destination identifier. If the filtering operationfield is set to source identifier, the frame is filtered by the originON_ID, and if the filtering operation field is set to destinationidentifier, the frame is filtered by the ON_ID of a designatedrecipient.

The tagging mechanism of the present invention enables an OLT and/or anoptical node (e.g., optical network unit or optical network terminator)to recognize the origination and/or destination of a particular frame.At a recipient optical node, acceptance or rejection of a received frameis based on its PON tag. For example, if the filtering operation fieldis set to source, an incoming frame is accepted at a recipient opticalnode if the ON_ID specified in the PON tag control information fielddoes not match the ON_ID of the recipient optical node. If, on the otherhand, the filtering operation field is set to destination, an incomingframe is accepted at a recipient optical node if the ON_ID specified inthe PON tag control information field matches the ON_ID of the recipientoptical node.

In another embodiment, the PON control information field only containstwo fields. A first field for specifying an ON_ID, and a second fieldfor specifying a mode. If the mode field is set for P2P service, arecipient optical node accepts an incoming frame if the ON_ID fieldmatches the ON_ID assigned to the recipient optical node. Otherwise, theincoming frame is rejected. If, on the other hand, the mode field is setfor shared service, a recipient optical node accepts an incoming frameif the ON_ID field does not match the ON_ID assigned to the recipientnode. Otherwise, the incoming frame is rejected.

At an OLT, the mode (i.e., P2P or shared services) influences thefiltering and forwarding processes for all received frames. For P2Pservices, the destination for each internal and external frame isdetermined. The ON_ID field is modified to designate the destinationoptical node. The mode field is also checked to ensure that it is set toP2P mode. Afterwards, each frame is forwarded one-by-one to itsdestination optical node.

For shared services, all internal frames are sent downstream to alloptical nodes operating on the shared path. The mode field is checked toensure that it is set to shared mode. Therefore, the present inventionenables all PON-tagged traffic to be reflected back if it is received ona shared communications path. As for an externally-generated frame, theOLT constructs a PON tag having a null ON_ID value or an universalidentifier. The mode field is set to shared mode, and the external frameis broadcast to all optical nodes operating on the shared path.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention. In the drawings, like reference numbers indicateidentical or functionally similar elements. Additionally, the leftmostdigit(s) of a reference number identifies the drawing in which thereference number first appears.

FIG. 1 illustrates an Ethernet-based optical network (EPON) according toan embodiment of the present invention.

FIG. 2 a illustrates an Ethernet frame for transport over an EPONaccording to an embodiment of the present invention.

FIG. 2 b illustrates a VLAN-tagged frame for transport over an EPONaccording to an embodiment of the present invention.

FIG. 2 c illustrates a PON-tagged frame for transport over an EPONaccording to an embodiment of the present invention.

FIG. 2 d illustrates a double tagged frame for transport over an EPONaccording to an embodiment of the present invention.

FIG. 2 e illustrates a double tagged frame for transport over an EPONaccording to another embodiment of the present invention.

FIG. 2 f illustrates a combined tagged frame for transport over an EPONaccording to an embodiment of the present invention.

FIG. 2 g illustrates a combined tagged frame for transport over an EPONaccording to an embodiment of the present invention.

FIG. 3 a illustrates a PON tag control information field of a frameaccording to an embodiment of the present invention.

FIG. 3 b illustrates a PON tag control information field of a frameaccording to another embodiment of the present invention.

FIG. 4 illustrates an operational flow for producing and/or updating aPON tag at an optical node according to an embodiment of the presentinvention.

FIG. 5 illustrates an operational flow for processing and/or updating aPON tag upon reception at an OLT according to an embodiment of thepresent invention.

FIG. 6 illustrates an operational flow diagram for processing and/orupdating a PON tag for transmission from an OLT according to anembodiment of the present invention.

FIG. 7 illustrates an operational flow diagram for processing and/orupdating a PON tag upon reception at an optical node according toanother embodiment of the present invention.

FIG. 8 illustrates an optical node according to an embodiment of thepresent invention.

FIG. 9 illustrates an OLT according to an embodiment of the presentinvention.

FIG. 10 illustrates an example computer system useful for implementingthe present invention.

DETAILED DESCRIPTION OF THE INVENTION Table of Contents

-   I. Introduction-   II. System Overview-   III. Overview of PON Tagging-   IV. Operational Flow for Optical Node PON Tag Construction-   V. Processing Upstream PON Tag by OLT-   VI. Processing Downstream PON Tag by an Optical Node-   VII. System Architecture for ONU and OLT-   VIII. Exemplary System Implementation    I. Introduction

The present invention implements a tagging mechanism that enables thephysical layer interface (PHY) to a passive optical network (PON) toemulate a point-to-point and/or shared communications link. The taggingmechanism specifies an optical node identifier and a transmission mode,which collectively influence filtering and forwarding processes for eachframe bearing the tagging mechanism. If, for example, the transmissionmode is set to shared services, a forwarding entity (e.g., bridge,router, etc.) broadcasts the frame to all optical nodes operating on ashared path, regardless of who transmitted the frame.

Accordingly, the tagging mechanism permits a PON-aware forwarding entityto interact with a PON segment as if the segment is a shared segmentand/or a point-to-point (P2P) segment even though a PON segment isneither. Unlike a conventional forwarding entity, the PON-awareforwarding entity of the present invention does not assume all peershave seen an upstream frame. A conventional forwarding entity will nothand a frame to a destination port if it is the incoming port thatreceived the frame. However, in the present invention, a PON-awareforwarding entity reflects back all PON-tagged frames received from ashared path.

The tagging mechanism also enables a forwarding entity to receive andprocess data and control messages as if they are coming from and goingto multiple ports at the PON PHY interface when in reality there is onlyone physical port. As such, the tagging mechanism allows a MAC controllayer to create virtual ports (also called “logical ports”) to trafficincoming and outcoming optical signals, and supply the virtual ports tothe forwarding entity for filtering and/or forwarding. In an embodiment,the PON PHY interface includes multiple physical ports. However, thepresent invention allows the MAC control layer to create additionalvirtual ports for one or more of the multiple physical ports, asrequired.

II. System Overview

FIG. 1 illustrates an Ethernet-based passive optical network (EPON) 100according to an embodiment of the present invention. Although thepresent invention is described with reference to an Ethernet-based PON,the present invention can also be implemented in other optical networks,including ATM-PON, active optical networks, etc.

EPON 100 includes an optical line terminal (OLT) 102 and one or morewidely distributed optical nodes (ON) 106 a–106 n (collectively referredto as “optical node (ON) 106”). EPON 100 can be implemented in any mediaand/or multimedia distribution network. Furthermore, it should beunderstood that the present invention can be implemented in any networkpermitting the exchange of voice, data, video, audio, messaging,graphics, other forms of media and/or multimedia, or any combinationthereof.

OLT 102 is centrally positioned to command and control interactions withand among multiple ON 106. OLT 102 manages upstream and/or downstreammodulation and bandwidth allocation, and executes rules and policies forclassifying and/or prioritizing communications with ON 106.

ON 106 includes an optical network unit (ONU), an optical networkterminator (ONT), or a combination of both. Each ON 106 is configurableto host one or more services to a subscriber end user. The servicesinclude telephony, television broadcasts, pay-for-view, video on demand,Internet communications (e.g., World Wide Web (WWW)), radio broadcasts,facsimile, file data transfer, electronic mailing services (email),messaging, video conferencing, live or time-delayed media feeds (suchas, speeches, debates, presentations, infomercials, news reports,sporting events, concerts, etc.), or the like. The subscriber end userincludes a home, business, multi-dwelling unit, building, or the like.

All communications transmitted in the direction from OLT 102 towards ON106 are referred to as being in the downstream. In an embodiment, thedownstream is divided into one or more downstream channels. Eachdownstream channel is configured to carry various types of informationto ON 106. Such downstream information includes television signals, datapackets (including IP datagrams), voice packets, control messages,and/or the like. In an embodiment, the downstream is formatted with anEthernet entity. However, the present invention can be configured tosupport other data formats as would be apparent to one skilled in therelevant art(s).

In an embodiment, OLT 102 implements time division multiplexing (TDM) totransmit continuous point-to-multipoint signals in the downstream. Inanother embodiment, OLT 102 implements wave division multiplexing (WDM)or dense wave division multiplexing (DWDM) to support communicationswith ON 106. In an embodiment, OLT 102 broadcasts signals to all ON 106or multicasts signals to two or more designated ON 106. In anotherembodiment, OLT 102 provides unicasts to a designated ON 106.

The upstream represents all communications from ON 106 towards OLT 102.Each upstream channel carries bursts containing frames of packets fromON 106 to OLT 102. In the upstream, each frequency channel is brokeninto multiple assignable slots, and each ON 106 send a time divisionmultiple access (TDMA) burst signal in an assigned slot. Each assignedslot is synchronized so that upstream packets from each ON 106 do notinterfere with each other. Hence, ON 106 transmits by using grantsissued by OLT 102. In another embodiment, WDM or DWDM is implemented tosupport communications with OLT 102.

The communication path (representing the upstream and downstream)between OLT 102 and ON 106 is referred to as the “PON segment.” In anembodiment, ON 106 and OLT 102 assemble and transmit a burst of frame(s)within the PON segment over a fiber-optic link. A passive opticalsplitter/combiner 104 is provided to demultiplex or multiplexbi-directional communications with each individual ON 106. In anotherembodiment, free-space optics (FSO) technology provides the transmissionmedium that carries optical signals between OLT 102 and ON 106.

OLT 102 also routes signals from ON 106 to a destined location overbackbone network 110. Backbone network 110, as well as the path betweenON 106 and the subscriber end-users, is part of a wired, wireless, orcombination of wired and wireless local area networks (LAN) or wide areanetworks (WAN), such as an organization's intranet, local internets, theglobal-based Internet (including the World Wide Web (WWW)), virtualprivate networks, or the like. Backbone network 110 supports wired,wireless, or both transmission media, including satellite, terrestrial(e.g., fiber optic, copper, twisted pair, coaxial, hybrid fiber-coaxial(HFC), or the like), radio, microwave, free-space optic, and/or anyother form or method of transmission.

As such, OLT 102 utilizes backbone network 110 to communicate withanother device or application external to EPON 100. The device orapplication can be a server, web browser, operating system, other typesof information processing software (such as, word processing,spreadsheets, financial management, or the like), television or radiotransmitter, a component of another optical network, or the like.

III. Overview of PON Tagging

The present invention provides a tagging mechanism to identify theorigin ON 106 (i.e., the ON 106 that originates the frames passed withina PON segment). In an embodiment, a “PON tag type” field and a “PON tagcontrol information” field (discussed with reference to “222” and “224”,respectively, in FIG. 2 c, below) are produced and/or activated to carryONU identification information. This embodiment of the present inventionenables the PON tag control information field and PON tag type field topropagate beyond the physical layer, such that the PON tag is availableat the desired layer within ON 106 (and OLT 102). Thus, the presentinvention avoids replicas of protocol stacks since the PON tag is notnecessarily placed in the preamble of a frame.

The tagging mechanism of the present invention is discussed withreference to FIGS. 2 a–2 g, which illustrate several embodiments of aframe that can be transported within EPON 100. First, FIG. 2 a shows aframe 200 a that does not include a tag. FIG. 2 b shows a frame 200 bthat includes frame format extensions that support virtual local areanetwork (VLAN) tagging on Ethernet networks. FIG. 2 c shows a frame 200c that includes frame format extensions to support PON tagging for anEPON. FIG. 2 d and FIG. 2 e show two embodiments (i.e., frame 200 d and200 e, respectively) that include both frame format extensions for VLANtagging and PON tagging. Finally, FIG. 2 f and FIG. 2 g show embodiments(i.e., frame 200 f and 200 g, respectively) that include a combinedframe format extension for VLAN tagging and PON tagging. As described ingreater detail, below, the present invention accommodates and processesall of the above-discussed tag types, in addition to any other type offrame presently known, or developed in the future, to be formatted fortransport over a PON segment.

Referring to FIG. 2 a, frame 200 a begins with a “preamble” field (Pre)202. Pre field 202 gives a recipient node (e.g., OLT 102 or ON 106) timeto recognize the presence of a signal before the frame data (shown as“data” field 212) arrives. Pre field 202 enables a recipient node tolock onto the signal, and synchronize the recipient node's clock withthe transmitting node's clock. Following Pre field 202 is a “start offrame delimiter” (SFD) field 204. SFD field 204 demarcates the beginningof relevant MAC frame information.

The first item of relevant MAC frame information is a “destinationaddress” (DA) field 206. DA field 206 identifies one or more networkcomponents designated to receive frame 200 a. The network component istypically customer premise equipment (CPE) associated with an ON 106. DAfield 206 can be an individual address for a single networkcomponent/node, a multicast address for a group of networkcomponent/nodes, or a broadcast address for all available networkcomponent/nodes.

Frame 200 a also contains a “source address” (SA) field 208 thatidentifies a network component that originated the frame. As discussed,the network component is typically CPE associated with an ON 106.

A “length/type” field 210 is also included to specify the quantity ofbytes present in data field 212. Data field 212 contains the MAC dataunit. Finally, a “frame check sequence” (FCS) field 214 supports errorchecking. In an embodiment, a cyclical redundancy check (CRC) value iscalculated when frame 200 a is assembled. The CRC value is appended atthe end of frame 200 a in FCS field 214. Upon receipt, a recipient nodeperforms identical checking and compares its result with the CRC value.If no match is found, frame 200 a is discarded or flagged as having anerror.

Referring to FIG. 2 b, frame 200 b includes frame format extensions thatsupport VLAN tagging on Ethernet networks. This format is defined inIEEE standard 802.3ac for VLAN tagging, and IEEE standard 802.1Q for theVLAN protocol. As shown, VLAN-tagged frame 200 b includes an identifier,or tag, that identifies the specific VLAN to which the frame belongs.The VLAN tag is shown as “VLAN tag type” field 216 and “VLAN tag controlinformation” field 218, and is inserted between SA field 208 andlength/type field 210. VLAN tag type field 216 indicates the presence ofa VLAN tag, and informs the recipient node that length/type field 210can be located at an offset of four bytes further into frame 200 b. Thevalue “81-00” represents the IEEE EtherType field assigned for use withthe IEEE standard 802.1Q. VLAN tag control information field 218contains the VLAN identifier (VID) which uniquely identifies the VLAN towhich the Ethernet frame 200 b belongs. VLAN tag control informationfield 218 also includes other information such as, a user priority fieldand a canonical format indicator (CFI), as defined in IEEE standard802.1Q.

Frame 200 b also includes a “PAD” field 220. PAD field 220 is optionaland used to ensure that frame 200 b satisfies minimum allowable sizerequirements. PAD field 220 is inserted and used to mitigate collisionwith another frame if frame 200 b is too short. In embodiments, PADfield 220 can also be included in frame 200 a, discussed above.

Referring to FIG. 2 c, frame 200 c shows frame format extensions forsupporting PON tagging within an EPON. The PON-tagged frame 200 cincludes a “PON tag type” field 222 and a “PON tag control information”field 224, which are referred to herein collectively as a “PON tag.” PONtag type field 222 is a two-byte field used to designate the presence ofa PON tag within frame 200 c. An IEEE EtherType field value can also beassigned for use with PON tag type 222. PON tag control informationfield 224 contains the control information for a specific ON 106.

In an embodiment, the control information includes an identifier (ON_ID)that uniquely identifies the origin ON 106. In an embodiment, one ormore ON_IDs are assigned to each ON 106 by OLT 102. In an embodiment,the ON_ID is an address for one or more physical or logical ports at thephysical interface of ON 106 to the PON segment. In another embodiment,the ON_ID is an address for one or more physical or logical ports at ON106 that serves as the interface with one or more MAC clients orsubscribers end users. In another embodiment, a separate ON_ID isassigned for the address at each port if multiple physical and/orlogical ports are configured at ON 106.

Other control information located in PON tag control information field224 includes priority data, etc. The length of PON tag controlinformation field 224 is approximately 2 bytes, but can be smaller orlarger if required.

In an embodiment, additional fields are added to the PON tag (i.e., PONtag type field 222 and PON tag control information field 224) to supportadditional services (such as, security) on an Ethernet network. As withframe 200 b, frame 200 c also includes PAD field 220 to ensure that theminimum allowable size requirements are satisfied.

Another embodiment of a PON-tagged frame (i.e., frame 200 d) is shown inFIG. 2 d. Frame 200 d includes frame format extensions that support bothVLAN tagging and PON tagging, and is therefore referred to as being adouble tagged frame 200 d. As shown, VLAN tag type field 216 and VLANtag control information field 218 follow SA field 208. Thereafter, PONtag type field 222 and PON tag control information field 224 arepositioned before length/type field 210. Accordingly, frame 200 dprovides control information for passing an Ethernet frame within a VLANas well as a PON segment.

The positions of the VLAN tag and PON tag are not necessarily orderdependent. Hence, FIG. 2 e shows another embodiment of a double taggedframe 200 e. In frame 200 e, the PON tag type field 222 and PON tagcontrol information field 224 precede the VLAN tag (i.e., 216 and 218).In another embodiment (not shown), the tag type fields (i.e., 216 and222) are positioned adjacent to each other and precede the controlinformation fields (i.e., 218 and 224), or vice versa.

FIG. 2 f. illustrates another embodiment of a PON-tagged frame (i.e.,frame 200 f). In this embodiment, the VLAN and PON tag type fields(i.e., 216 and 222) are represented as a single combined tagspecification, shown as a single combined tag type field 226. Combinedtag type field 226 designates the presence of a VLAN tag, PON tag, orboth. The control information for the VLAN tag and PON tag is providedin VLAN tag control information field 218 and PON tag controlinformation field 224. Therefore, frame 200 f enables an Ethernet frameto be passed within a VLAN and/or PON segment depending on the contentsof fields 226, 218 and 224.

As previously discussed, the positions of the VLAN tag and PON tag arenot necessarily order dependent. Hence as shown in FIG. 2 g, combinedtagged frame 200 g shows PON tag control information field 224 precedingVLAN tag control information field 218. In another embodiment (notshown), VLAN tag control information field 218 and/or PON tag controlinformation field 224 precedes combined tag type field 226.

An embodiment of PON tag control information field 224 is illustrated inFIG. 3 a. As shown, PON tag control information field 224 includes a“filtering operation” (Op) field 302, a “mode” field 304, and a “tagidentifier” (TID) field 306. TID field 306 contains an ON_ID asdiscussed above with reference to FIG. 2 c. Mode field 304 specifieswhether, for example, frame 200 c is to be, or has been, transportedover a point-to-point communications path (i.e., P2P mode), or a sharedcommunications path (i.e., shared mode). Op field 302 specifies whether,for example, frame 200 c is to be filtered by a source identifier ordestination identifier. The source identifier refers to the origin ON106, and the destination identifier refers to a designated recipient(s)ON 106. The source identifier and/or destination identifier arespecified in TID field 306.

In an embodiment, OP field 302 and mode field 304 overlap infunctionality and, thus, is reduced to only one field. FIG. 3 b shows anembodiment of PON tag control information field 224 that illustrates theoverlapping functionality. As shown, Op field 302 has been eliminated.Mode field 304 specifies the transport mode as being P2P or shareddistribution. As described in greater detail below, if mode field 304 isdesignated as P2P, the frame (e.g., frame 200 c) is filtered by adestination identifier. Otherwise, the frame is filtered by a sourceidentifier.

Hence, the PON tag of the present invention can be the ON_ID of theorigin ON 106 or a derivative of the ON_ID value. In an embodiment, thePON tag contains additional fields for security and/or other services inaddition to the forwarding fields described with reference to FIG. 3 aand FIG. 3 b. Moreover, as described above, the tag type information ofthe present invention is carried in a type field (i.e., PON tag typefield 222) that is similar to, but distinguishable from, a VLAN tag(i.e., tag type field 216). However, in another embodiment, PON tagginginformation is carried in a preamble (e.g., Pre field 202). In otherembodiments, the PON tagging information is positioned before DA field206, between DA field 206 and SA field 208, or at other locations withinthe tagged MAC frame.

IV. Operational Flow for Optical Node PON Tag Construction

As described above, the present invention implements a tagging mechanismfor tracking the origin and/or destination of a frame within a PONsegment, such as the PON segment shown in FIG. 1. Referring to FIG. 4,flowchart 400 represents the general operational flow of an embodimentof the present invention. More specifically, flowchart 400 shows anexample of a control flow for producing and/or updating a PON tag at anorigin ON 106.

The control flow of flowchart 400 begins at step 401 and passesimmediately to step 403. At step 403, an optical node (such as, ON 106)accesses information to be formatted and transmitted upstream to an OLT(such as, OLT 102). The information primarily comprises MAC clientinformation that includes information from a subscriber end user (asshown in FIG. 1), which includes data, voice, and/or video. The MACclient information can also include control messages generated at theoptical node (e.g., ON 106). For example, the control message can be arequest to OLT 102 for additional bandwidth.

The information is packetized, if it is not already, into a service dataunit. The optical node (e.g., ON 106) prepares a data frame (such as,for example, frame 200 c described above with reference to FIG. 2 c).The data frame (e.g., frame 200 c) includes the service data unit indata field 212.

At step 406, a PON tag (also referred to as “Ptag”) is produced and/oractivated. For example referring back to the embodiment described withreference to FIG. 2 c, PON tag type field 222 is added to the data frame(e.g., frame 200 c) to designate the presence of a PON tag.Additionally, PON tag control information field 224 is added to specifythe PON tag control information, namely the origin ON_ID. As describedwith reference to TID field 306 in FIG. 3 a, the ON_ID can be theaddress for the port (logical or physical) that the origin ON_IDutilizes to transmit the PON-tagged frame. Alternatively, the ON_ID canbe the address for the port that ON_ID utilizes to service a subscriberend user or MAC client associated with the PON-tagged frame. Thus, in anembodiment, the present invention implements a tagging mechanism thatonly specifies the origin ON_ID. In another embodiment (describedbelow), the tagging mechanism can also specify a destination ON_ID.Accordingly, the tagging mechanism of the present invention can specifythe origin ON_ID, a destination ON_ID, or both.

After the data frame has been assembled into PON tagged frame (e.g.,frame 200 c), the control flow passes to step 409. At step 409, thePON-tagged frame is transmitted upstream to, for example, OLT 102. Whentransmitted in the upstream, the PON tag is referred to as an upstreamPON tag (or Utag).

At step 412, a check is made for the presence of additional informationto be transmitted upstream. If additional information is present, thecontrol flow returns to step 403. Otherwise, the control flow ends asindicated at step 495.

V. Processing Upstream PON Tag by OLT

The control flow of FIG. 4 describes an exemplary tagging solution formarking a frame to designate its origin optical node (e.g., ON 106). Asthe frame is transported within a PON segment, a recipient can easilyidentify the origin of the frame. Referring to FIG. 5, flowchart 500represents the general operational flow of another embodiment of thepresent invention. More specifically, flowchart 500 shows an example ofa control flow for processing and/or updating a PON tag at an OLT (e.g.,OLT 102) prior to passing the frame having the PON tag to a forwardingentity.

The control flow of flowchart 500 begins at step 501 and passesimmediately to step 503. At step 503, an OLT (e.g., OLT 102) receives anupstream frame from the PON segment. The upstream frame is one of theembodiments of PON-tagged frames described above (i.e., frame 200 c,frame 200 d, frame 200 e, frame 200 f, or frame 200 g of FIGS. 2 c–2 g).

The physical interface to OLT 102 supports P2P and/or sharedcommunications. Conventionally, a PON segment is neither a P2P segmentnor a shared segment. However, as described in greater detail below withreference to FIG. 9, the present invention enables an OLT (such as, OLT102) to configure and/or reconfigure its PON segment to emulate a P2Pservice, downstream broadcast service, shared service, or anycombination of the above. In an embodiment, OLT 102 includes a physicalport that is adaptable to be designated as a P2P and/or shared port. Inanother embodiment, OLT 102 includes a single physical port that can beconfigured and/or reconfigured into multiple logical or virtual ports.

In other words, although the physical transmission medium (e.g., a fiberoptic cable, free space optical link, etc.) is coupled to a singlephysical input/output port of OLT 102, OLT 102 or system componentsassociated with OLT 102 are enabled to parse and/or process theinformation exchanged via the single physical port as if the informationis being exchanged over separate physical ports. By arbitratingbandwidth among the plurality of ON 106 with respect to time, frequency,code, and/or the like, OLT 102 can create a plurality of upstream and/ordownstream channels. Although these channels share a common physicalport at OLT 102, the information exchanged over the single physical portis parsed and/or processed according to the designated channel (e.g., achannel identifier in the header of an upstream frame). Assigning eachchannel to a designated logical or virtual port, OLT 102 is enabled tooperate as if the information is being exchanged over differentchannels, with each channel being treated as if it is being servicedover a dedicated logical port at OLT 102. As such, the physicalinterface to OLT 102 includes, in embodiments, one or morevirtual/logical ports for P2P service, one or more virtual/logical portsfor shared service, or a combination of both.

If a port (physical or logical) receives a PON-tagged frame from ON 106,the port is referred to as being part of a PON-enabled (or tag-enabled)physical interface because the port is linked to an optical elementcapable of producing and/or passing frames that are tagged according tothe present invention. If a port (physical or logical) exclusivelyreceives frames lacking a PON tag, the port is referred to as being partof a traditional physical interface because the port is not linked to anoptical element capable of producing and/or passing frames that aretagged according to the present invention. It should be understood theexpression “PON-enabled,” as used herein, is not intended to be limitedto passive optical networks. As previously discussed in alternateembodiments, the present invention can be implemented in other types ofnetworks.

Accordingly, in an embodiment, OLT 102 is configured to receive and/ortransmit frames only on a PON-enabled physical interface. In anotherembodiment, OLT 102 is configured to receive frames and/or transmit froma traditional physical interface and a PON-enabled physical interface.In an embodiment, OLT 102 includes an interface to backbone 110, whichis not a PON-enabled interface, and at least one PON-enabled interface.A frame coming from the “non-PON-enabled” interface to backbone 110 isreferred to as an external frame. A frame arriving from the PON-enabledinterface is referred to as an internal frame. All internal frames in aPON segment are PON-tagged frames. External frames are not PON-taggedframes.

At step 506, the OLT (e.g., OLT 102) detects or searches for thepresence of a PON tag. Referring back to FIGS. 2 c–2 g in an embodiment,a PON tag type field 222 is included to designate the presence of a PONtag. Thus, if PON tag type field 222 is found, the frame is determinedto be a PON-tagged frame (e.g., frame 200 c). The control flow wouldthen pass to step 509.

Otherwise, if no PON tag is detected, the frame is determined to be anon-PON-tagged frame (such as, frame 200 a or 200 b). The frame isconsidered to have originated external to the PON segment or from anon-PON enabled port. Therefore, the control flow would pass to step512. In an embodiment, if the PON tag (e.g., PON tag control informationfield 224) for a PON-tagged frame (e.g., frame 200 c) is missing, lost,or damaged, the OLT (e.g., OLT 102) discards the frame if it goes to thesame PON interface, or treats the frame as a non-PON-tagged frame if itgoes to an external interface.

At step 509, the OLT (e.g., OLT 102) extracts or derives the PON tagvalue from PON tag control information field 224. This value is used toprepare a forwarding tag (or Ftag) that is appended to frame 200 c. Inan embodiment, the forwarding tag is the upstream PON tag. In anotherembodiment, the forwarding tag is identical to the ON_ID specified inthe PON tag. In another embodiment, the forwarding tag is a derivativeof any information in the upstream PON tag. In another embodiment, theforwarding tag is derived from any information in the original frame(including the upstream PON tag), or additional state in OLT 102.

At step 512, the OLT (e.g., OLT 102) constructs a PON tag for anon-PON-tagged frame. However since the origin optical node (e.g., ON106) is unknown or the origin node is external to the destination PONsegment, the ON_ID is set to a null value to thereby produce a “null PONtag.” In an embodiment, a universal identifier (i.e., “universal ON_ID”)is specified for all broadcast or multicast operations. This universalidentifier is also used as the null PON tag value. The null PON tagvalue is used, at step 512, to prepare a forwarding tag that is appendedto the frame. As intimated, the forwarding tag can be identical to, or aderivative of, the null ON_ID value. For example, referring back to FIG.3 b , the mode field 304 can be set to shared distribution or P2P. Ifthe frame is being sent to an optical node (e.g., ON 106) having a P2Pcommunications link with the OLT (e.g., OLT 102), the TID field 306 isset to the ON_ID for the destination ON 106, and the mode is set to P2P.Thus, the PON tag would have mode field 304 and TID field 306 values of“(P2P, destination ON_ID).” If, however, the frame is being sent anoptical node (e.g., ON 106) operating on a shared communications pathwith the OLT (e.g., OLT 102) (or if mode is unknown), the mode field 304and TID field 306 values would read as “(shared, universal ON_ID).”

It should be understood that a multicast or broadcast frame can be senton a P2P path to each member of the multicast or broadcast group, or ona shared path to all optical nodes (e.g., ON 106) operating on theshared path. If sent to all optical nodes operating on a shared path,the optical nodes that are members of the multicast group would acceptthe frame, and the non-members would reject the frame. Similarly, itshould be understood that a unicast frame can be sent on a P2P path tothe designated optical node (e.g., ON 106), or on a shared path to alloptical nodes (e.g., ON 106) operating on the shared path. If sent toall optical nodes operating on a shared path, the designated recipientof the unicast would accept the frame, and all other optical nodes onthe shared path would reject the frame.

At step 515, the forwarding-tagged frame is queued according to theincoming port (i.e., physical port or logical port) of the physicalinterface that received the frame. In an embodiment, OLT 102 matches theincoming port to the frame upon receipt. In another embodiment, theincoming port is detected or extracted from one or more fields withinthe frame (e.g., from PON tag control information field 224). In anotherembodiment, OLT 102 has separate and parallel processing paths for allavailable ports, and queues the frames accordingly.

At step 518, the queues (designating a respective incoming port) areemptied to pass the upstream frames to a forwarding entity. In anembodiment based on logical ports, the upstream frames are passed withthe forwarding tags. In an embodiment based on multiple physical ports,the upstream frames are passed over designated physical interfaces withthe forwarding entity. After the upstream frames are passed to theforwarding entity, the control flow ends as indicated by step 595.

Referring, now, to FIG. 6, flowchart 600 represents the generaloperational flow for processing and/or updating a PON tag fortransmission from an OLT (e.g., OLT 102), according to an embodiment ofthe present invention. More specifically, flowchart 600 shows an exampleof a control flow for processing and/or updating a PON tag after beingpassed to a forwarding entity associated with an OLT (e.g., OLT 102).

The control flow of flowchart 600 begins at step 601 and passesimmediately to step 603. At step 603, the forwarding entity receives aframe. In an embodiment based on logical ports, the frame includes theforwarding tag. In an embodiment based on multiple physical ports, theforwarding entity notes the incoming port that received the frame, sincethe frames are queued by incoming port.

At step 606, the forwarding entity determines the destination port(s)for the frame. In an embodiment, the forwarding entity uses thedestination address (i.e., DA field 206) to query a look-up orforwarding table to determine the destination port(s). The table can beprogrammable to learn destination addresses and corresponding port(s).

At step 609, the forwarding entity considers the frame's incoming porttype (i.e., a traditional physical interface or a PON-enabled physicalinterface). As discussed, this information is noted at step 603 from thequeue. In an embodiment, the forwarding entity learns that a specificqueue is associated with a specific port type. In another embodiment, atag is appended to the frame to designate the incoming port prior tobeing handed to the forwarding entity, and the forwarding entity learnsthe port type. Alternatively, a tag can be appended, prior to deliveringthe frame to the forwarding entity, to designate the incoming port type.In another embodiment, a learning table is queried and/or updated todetermine the port type from the incoming port. As would be apparent toone skilled in the relevant art(s), other variants, methodologies, ortechniques can be used to permit the forwarding entity to become awareof the incoming port or port type.

If the incoming port is PON-enabled, at step 612, the incoming port isincluded as a destination port, regardless of whether it had beendetermined to be a destination port at step 606. As a result, aPON-tagged frame is always reflected back to the origin ON 106. In anembodiment, all upstream traffic is reflected back on all PON-enabledports. In another embodiment, upstream traffic is only reflected back ona PON-enabled port configured for shared distributions.

On the other hand, if the incoming port is a traditional port, thecontrol flow passes immediately to step 615. Therefore, since aforwarding entity conventionally does not transmit signals back on anincoming port, the frame is not returned to the incoming port if it isnot included in the destination port(s).

At step 615, the frame is queued according to its destination port(s).The queues are subsequently emptied for further processing. If adestination port is a PON-enabled port, the OLT (e.g., OLT 102) verifiesor prepares a PON tag for downstream transmission. In the downstream,the PON tag is referred to as the downstream PON tag (or Dtag).

Referring back to FIG. 3 b, a representative PON tag includes mode field304 denoted as “shared” or “P2P,” and TID field 306 specifying an originON_ID. If mode field 304 is set to “P2P,” the forwarding entitydetermines the PON segment destination and OLT 102 modifies, ifnecessary, TID field 306 to specify the “destination” ON_ID. Themodified tag “(P2P, destination ON_ID)” becomes the downstream PON tagthat is passed with the frame to its downstream destination. Asdiscussed above if the frame is externally generated or from an unknownsource, the PON tag would already read “(P2P, destination ON_ID).”Therefore, no modification should be required.

On the other hand if mode field 304 is set to “shared,” the forwardingentity determines the group membership for the multicast or broadcast,but OLT 102 does not modify the TID field 306. The downstream PON tag isthe same as the upstream PON tag, namely “(shared, origin ON_ID)” if theframe is PON-originated or “(shared, universal ON_ID)” if externallygenerated or from an unknown source.

If a destination port is a traditional port or if the frame is beingsent to a higher layer application or MAC client of the OLT (e.g., OLT102), the PON tag is removed. Moreover if at any step a PON-tagged frameis passed to a traditional device (e.g., bridge, router, etc.) that isnot PON-aware, the PON tag is eliminated. After the frame has beenpassed to its destination port(s), the control flow ends as indicated bystep 695.

The present invention, therefore, provides a PON-aware forwarding entityhaving the capability to interact with a PON segment as if the segmentis one of the known segment types, namely shared, P2P, or both. Unlike aconventional forwarding entity, the PON-aware forwarding entity of thepresent invention does not assume all peers have seen an upstream frame.A conventional forwarding entity will not hand a frame to a destinationport if it is the incoming port that received the frame. However, in thepresent invention, a PON-aware forwarding entity reflects back allPON-tagged frames received over a shared path.

VI. Processing Downstream PON Tag by an Optical Node

As discussed, FIG. 4 describes an embodiment for producing and/orupdating a PON tag for upstream transmissions. FIGS. 5–6 describeembodiments for processing and/or updating a PON tag at an OLT (e.g.,OLT 102). Referring, now, to FIG. 7, flowchart 700 represents thegeneral operational flow of the reception process at an optical node(e.g., ON 106) according to an embodiment of the present invention. Morespecifically, flowchart 700 shows an example of a control flow forprocessing and/or updating a PON tag upon delivery at an optical node(e.g., ON 106).

The control flow of flowchart 700 begins at step 701 and passesimmediately to step 703. At step 703, an optical node (e.g., ON 106)receives a frame (e.g., frame 200 c, 200 d, 200 e, etc.) from adownstream channel. At step 706, the optical node (e.g., ON 106) detectsor reads a PON tag appended to the frame. As discussed, in anembodiment, PON tag type field 222 designates the frame as being aPON-tagged frame.

At step 709, the optical node (e.g., ON 106) determines whether theframe has been distributed in P2P or shared mode. In an embodiment, modefield 304 is processed to determine whether the frame is designated asbeing in P2P or shared mode. If P2P mode is determined, the control flowpasses to step 712. Otherwise, the control flow passes to step 715 forprocessing shared distributions.

At step 712, the optical node (e.g., ON 106) determines whether it isthe intended recipient of the frame. As discussed above, a PON-taggedframe sent downstream in P2P mode includes mode field 304 and TID field306 values reading “(P2P, destination ON_ID). If the destination ON_IDspecified in TID field 306 does not match the ON_ID of the recipientoptical node (e.g., ON 106), the optical node is not the intendedrecipient. As such, the frame is discarded at step 718. Otherwise, theframe is accepted at step 721.

Shared mode distributions are processed at step 715. When executed, step715 enables a recipient optical node (e.g., ON 106) to determine whetherit originated a PON-tagged frame (e.g., frame 200 c, 200 d, 200 e, etc.)received in the downstream. As discussed above, a PON-tagged frame senton a shared downstream includes mode field 304 and TID field 306 valuesreading “(shared, origin ON_ID)” for PON-originated frames and “(shared,universal ON_ID)” for externally generated or unknown sourced frames.Processing TID field 306, the optical node (e.g., ON 106) determines ifits ON_ID(s) matches and hence, whether it is the origin optical node(i.e., it originated the PON-tagged frame). If the recipient opticalnode is the origin optical node, the frame is rejected at step 718.Otherwise, it is accepted, at step 721, because the frame is determinedto be produced by a peer optical node (e.g., ON 106).

This process is effective for supporting reflect-back operations of aPON-enabled OLT (e.g., OLT 102). The reflect-back operations permit oneor more peer optical nodes (e.g., ON 106) to remain aware of signalstransmitted upstream to the OLT (e.g., OLT 102), especially on a sharedcommunications path. Additionally, reflecting-back permits a peeroptical node on a shared path to receive the frame if an intendeddestination is one of the subscriber end users of the peer optical node.Conversely, traditional OLT-forwarding entities do not return the frameto the shared path peers because it assumes that the peers have alreadyseen the frame.

If the frame (received from a shared or P2P path) is accepted, then atstep 724, the PON tag is deactivated or removed from the frame and sentto a higher layer application or MAC client for further processing.Afterwards, the control flow ends as indicated by step 795.

As described above, TID field 306 designates the ON_ID as being a singlenode identifier. In other words, TID field 306 specifies an identifierfor a single optical element of system 100 (namely, one of ON 106). Itshould be understood that the single node designation of TID field 306has been described by way of example. In embodiments of the presentinvention, the contents or value of TID field 306 is easily extendableto support a multi-node designation. If, for example, a single ON 106belongs to one or more groups of ON 106, a membership identifier isspecified for each group. The single ON 106, therefore, retains a listof membership identifiers for each of these groups. As a frame isprocessed as described herein, a membership identifier is included inTID field 306 to specify source and/or destination identifiers for amulticast according to the embodiments herein described. For example, ON106 is enabled to perform a check rule to either select a membershipidentifier to produce a PON tag prior to sending a frame, or to verify amembership identifier to process a PON tag prior to accepting orrejecting a frame. Similarly, OLT 102 is enabled to perform a check ruleto select a membership identifier while processing or producing adownstream PON tag, as discussed above.

VII. System Architecture for ONU and OLT

FIG. 8 illustrates an embodiment of ON 106 that can be used to implementthe present invention as described with reference to FIGS. 1–7. ON 106includes a physical layer interface (PHY) 802, media access control(MAC) layer 804, and MAC control layer 806. In an embodiment, PHY 802,MAC 804, and MAC control 806 are configured to comply with thespecifications of IEEE standard 802.3 and/or 803.3ah.

PHY 802 serves to receive and transmit signals (e.g., voice, data,video, etc.) among the subscriber end-users (shown as MAC client 808),as discussed above with reference to FIG. 1. As discussed above, ON 106utilizes one or more physical or logical ports to communicate with OLT102 over the PON segment. Additionally, one or more physical or logicalports are used to communicate with its end users (MAC client 808). PHY802 also supports full duplex communications (e.g., voice, data, video,control messages) with OLT 102. Hence, PHY 802 is configurable tosupport electronic, electromagnetic, optical signals, and/or the like.PHY 802 modulates signals to be transmitted as bursts, and demodulatessignals that it receives. In an embodiment, PHY 802 performs errorchecking on a received signal and/or discard the signal if errors arefound.

Signals from PHY 802 are passed to MAC 804 for Ethernet protocolprocessing. It should be understood that the above reference to Ethernetprotocol processing is provided by way of example. Hence, in alternateembodiments, MAC 804 performs protocol processing in compliance withother types of communication protocols governing multimedia distributionnetworks.

MAC control 806 receives frames from MAC 804 and integrates the taggingmechanism of the present invention. In an embodiment, MAC 804 takes aframe coming from MAC client 808, and appends or inserts a PON tag(e.g., PON tag type field 222 and PON tag control information field224). The resulting PON tagged-frame (e.g., frame 200 c, 200 d, 200 e,etc.) is queued for delivery to PHY 802.

During registration with OLT 102, ON 106 receives instructions (e.g.,ON_ID and/or membership identifier values to use in the PON tag) toestablish and format the ports. At this time, ON 106 can requestadditional ports.

FIG. 9 illustrates an OLT 102 according to an embodiment of the presentinvention. OLT 102 includes a physical layer interface (PHY) 902, mediaaccess control (MAC) layer 904, MAC control layer 906, a forwardingentity 908, and a forwarding table 914. In an embodiment, PHY 902, MAC904, and MAC control 906 are configured to comply with the requirementsof IEEE standard 802.3, and forwarding entity 908 is configured toconform to IEEE standard 802.1D, with additional functionality accordingto the present invention.

PHY 902 supports full duplex communications (e.g., voice, data, video,control messages) with ON 106 (or ONU 800). Accordingly, PHY 902transmits and receives optical signals via the PON segment. PHY 902demodulates the signals to decompress and/or extract voice, data, video,requests, other control messages, and/or the like. In an embodiment, PHY902 performs error checking, if required. If errors are detected, theburst is discarded. In another embodiment, the burst is flagged and theerror is corrected at MAC 904.

Therefore, MAC 904 performs Ethernet protocol processing. As discussedabove, it should be understood that the above reference to Ethernetprotocol processing is provided by way of example. Hence, in alternateembodiments, MAC 904 performs protocol processing in compliance withother types of communication protocols governing multimedia distributionnetworks.

MAC control 906 processes, updates, and/or constructs the PON tag of thepresent invention. In an embodiment, MAC control 906 reads or extractsthe PON tag received from PHY 902 and produced by the origin ON 106, andprepares a forwarding tag, as described above. If MAC control 906receives a frame lacking a PON tag (e.g., an external frame), a null PONtag is constructed, as described above. The null PON tag is appended tothe frame as its forwarding tag. The frame (with forwarding tag) isqueued according to the incoming port that received the frame from theupstream.

Forwarding entity 908 (such as a bridge, router, etc.) reads destinationaddress (e.g., DA field 206) and queries forwarding table 914 todetermine the destination port(s) for each frame. Forwarding table 914includes disposition instructions for forwarding information (e.g.,frame 200 a, 200 b, 200 c, 200 d, etc.) delivered to OLT 102. Thedisposition instructions include, but are not limited to, a destinationport (physical or logical) corresponding to a destination or sourceaddress, port mirror requirements, frame handling requirements,prioritization, multicast group membership, and/or like features. In anembodiment, forwarding table 914 is programmable to learn portassociations with MAC or PON addresses, and/or forwarding table 914 isresponsive to periodic or on-demand updates, regarding the portassociations, from an operator interface, software application, oranother control system. In an embodiment, forwarding table 914 isprogrammable to store a PON tag with the associated frame.

Upon receipt of disposition instructions, forwarding entity 908 filtersand queues the frames to be forwarded to the destination port(s).Forwarding entity 908 is a PON-aware forwarding entity, and therefore,forwarding entity 908 forwards back a frame to its incoming port if theincoming port is a PON port. Additionally, forwarding entity 908includes a plurality of physical or logical ports for downstreamtransmissions to ON 106. One or more shared physical or logical portssupport shared communications, and multiple physical or logical portssupport P2P communications. Each ON 106 has a designated physical orlogical port for P2P communications. Thus, in an embodiment OLT 102includes a single physical port to the PON segment, multiple logicalports configured for P2P and/or shared paths, and another physical portto backbone 110. In another embodiment, OLT 102 includes multiplephysical ports with or without logical ports.

After the frames have been filtered into the appropriate destinationport, the frames (with their appended forwarding PON tags) are forwardedto MAC control 906. MAC control 906 updates or prepares a downstream PONtag (or Dtag) for each frame. The frame then passes to MAC 904 forfurther formatting or protocol processing, and to PHY 902 to betransmitted to its downstream destination.

VIII. Exemplary System Implementation

FIGS. 1–9 are conceptual illustrations allowing an easy explanation ofthe present invention. It should be understood that embodiments of thepresent invention could be implemented in hardware, firmware, software,or a combination thereof. In such an embodiment, the various componentsand steps would be implemented in hardware, firmware, and/or software toperform the functions of the present invention. That is, the same pieceof hardware, firmware, or module of software could perform one or moreof the illustrated blocks (i.e., components or steps).

Additionally, the present invention can be implemented in one or morecomputer systems capable of carrying out the functionality describedherein. Referring to FIG. 10, an example computer system 1000 useful inimplementing various components or steps of the present invention isshown. Various embodiments of the invention are described in terms ofthis example computer system 1000. After reading this description, itwill become apparent to one skilled in the relevant art(s) how toimplement the invention using other computer systems and/or computerarchitectures.

The computer system 1000 includes one or more processors, such asprocessor 1004. Processor 1004 can be a special purpose or a generalpurpose digital signal processor. Processor 1004 is connected to acommunication infrastructure 1006 (e.g., a communications bus, crossoverbar, or network). Various software implementations are described interms of this exemplary computer system. After reading this description,it will become apparent to a one skilled in the relevant art(s) how toimplement the invention using other computer systems and/or computerarchitectures.

Computer system 1000 also includes a main memory 1008, preferably randomaccess memory (RAM), and can also include a secondary memory 1010. Thesecondary memory 1010 can include, for example, a hard disk drive 1012and/or a removable storage drive 1014, representing a floppy disk drive,a magnetic tape drive, an optical disk drive, etc. The removable storagedrive 1014 reads from and/or writes to a removable storage unit 1018 ina well-known manner. Removable storage unit 1018 represents a floppydisk, magnetic tape, optical disk, etc. As will be appreciated, theremovable storage unit 1018 includes a computer usable storage mediumhaving stored therein computer software (e.g., programs or otherinstructions) and/or data.

In alternative implementations, secondary memory 1010 includes othersimilar means for allowing computer software and/or data to be loadedinto computer system 1000. Such means include, for example, a removablestorage unit 1022 and an interface 1020. Examples of such means includea program cartridge and cartridge interface (such as that found in videogame devices), a removable memory chip (such as, an EPROM or PROM) andassociated socket, and other removable storage units 1022 and interfaces1020 which allow software and data to be transferred from the removablestorage unit 1022 to computer system 1000.

Computer system 1000 can also include a communications interface 1024.Communications interface 1024 allows software and/or data to betransferred between computer system 1000 and external devices. Examplesof communications interface 1024 include a modem, a network interface(such as an Ethernet card), a communications port, a PCMCIA slot andcard, etc. Software and data transferred via communications interface1024 are in the form of signals 1028 which can be electronic,electromagnetic, optical, or other signals capable of being received bycommunications interface 1024. These signals 1028 are provided tocommunications interface 1024 via a communications path (i.e., channel)1026. Communications path 1026 carries signals 1028 and can beimplemented using wire or cable, fiber optics, a phone line, a cellularphone link, an RF link, free-space optics, and/or other communicationschannels.

In this document, the terms “computer program medium” and “computerusable medium” are used to generally refer to media such as removablestorage unit 1018, removable storage unit 1022, a hard disk installed inhard disk drive 1012, and signals 1028. These computer program productsare means for providing software to computer system 1000. The invention,in an embodiment, is directed to such computer program products.

Computer programs (also called computer control logic or computerreadable program code) are stored in main memory 1008 and/or secondarymemory 1010. Computer programs can also be received via communicationsinterface 1024. Such computer programs, when executed, enable thecomputer system 1000 to implement the present invention as discussedherein. In particular, the computer programs, when executed, enable theprocessor 1004 to implement the processes of the present invention, suchas the method(s) implemented using components of OLT 102 and/or ON 106described above, such as various steps of methods 400, 500, 600, and/or700, for example. Accordingly, such computer programs representcontrollers of the computer system 1000.

In an embodiment where the invention is implemented using software, thesoftware can be stored in a computer program product and loaded intocomputer system 1000 using removable storage drive 1014, hard drive1012, interface 1020, or communications interface 1024. The controllogic (software), when executed by the processor 1004, causes theprocessor 1004 to perform the functions of the invention as describedherein.

In another embodiment, the invention is implemented primarily inhardware using, for example, hardware components such as applicationspecific integrated circuits (ASICs). Implementation of the hardwarestate machine so as to perform the functions described herein will beapparent to one skilled in the relevant art(s).

In yet another embodiment, the invention is implemented using acombination of both hardware and software.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample, and not limitation. It will be apparent to one skilled in therelevant art(s) that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Moreover, it should be understood that the method, system, and computerprogram product of the present invention could be implemented in anymulti-nodal communications environment governed by centralized nodes.The nodes include, but are not limited to, cable modems and headends, aswell as communication gateways, switches, routers, Internet accessfacilities, servers, personal computers, enhanced telephones, personaldigital assistants (PDA), televisions, set-top boxes, or the like. Thus,the present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

1. A method for processing information from a downstream path of anoptical network, comprising the steps of: accessing, at a recipientoptical node, a frame having an optics control tag embedded therein;determining a distribution mode for said frame; detecting an opticalnode identifier from said optics control tag; and accepting said framein response to detecting said distribution mode being designated for ashared service and to detecting said optical node identifier notmatching an optical node identifier assigned to said recipient opticalnode.
 2. The method of claim 1, further comprising the step of:accepting said frame in response to detecting said distribution modebeing designated for a point-to-point service and to detecting saidoptical node identifier matching the optical node identifier assigned tosaid recipient optical node.
 3. An optical network element forprocessing information from a downstream path of an optical network,comprising: interfacing means for accessing a frame from acommunications path of the optical network; an optics tag detector fordetecting a presence of an optics control tag appended to said frame,wherein said optics tag detector is responsive to determining adistribution mode for said optics control tag, wherein said optics tagdetector is responsive to detecting an optical node identifier from saidoptics control tag; and a frame controller for accepting said frame inresponse to said optics tag detector detecting said distribution modebeing designated for a shared service and to detecting said optical nodeidentifier not matching an optical node identifier assigned to theoptical network element.
 4. The optical network element of claim 3,wherein said frame controller is responsive to accepting said frame inresponse to said optics tag detector detecting said distribution modebeing designated for a point-to-point service and to detecting saidoptical node identifier matching the optical node identifier assigned tothe optical network element.